Astrochemistry

Astrochemistry is de study of de abundance and reactions of mowecuwes in de Universe, and deir interaction wif radiation.[1] The discipwine is an overwap of astronomy and chemistry. The word "astrochemistry" may be appwied to bof de Sowar System and de interstewwar medium. The study of de abundance of ewements and isotope ratios in Sowar System objects, such as meteorites, is awso cawwed cosmochemistry, whiwe de study of interstewwar atoms and mowecuwes and deir interaction wif radiation is sometimes cawwed mowecuwar astrophysics. The formation, atomic and chemicaw composition, evowution and fate of mowecuwar gas cwouds is of speciaw interest, because it is from dese cwouds dat sowar systems form.

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As an offshoot of de discipwines of astronomy and chemistry, de history of astrochemistry is founded upon de shared history of de two fiewds. The devewopment of advanced observationaw and experimentaw spectroscopy has awwowed for de detection of an ever-increasing array of mowecuwes widin sowar systems and de surrounding interstewwar medium. In turn, de increasing number of chemicaws discovered by advancements in spectroscopy and oder technowogies have increased de size and scawe of de chemicaw space avaiwabwe for astrochemicaw study.

Spectroscopy was first used to distinguish between different materiaws after de rewease of Charwes Wheatstone's 1835 report dat de sparks given off by different metaws have distinct emission spectra.[4] This observation was water buiwt upon by Léon Foucauwt, who demonstrated in 1849 dat identicaw absorption and emission wines resuwt from de same materiaw at different temperatures. An eqwivawent statement was independentwy postuwated by Anders Jonas Ångström in his 1853 work Optiska Undersökningar, where it was deorized dat wuminous gases emit rays of wight at de same freqwencies as wight which dey may absorb.

This spectroscopic data began to take upon deoreticaw importance wif Johann Bawmer's observation dat de spectraw wines exhibited by sampwes of hydrogen fowwowed a simpwe empiricaw rewationship which came to be known as de Bawmer Series. This series, a speciaw case of de more generaw Rydberg Formuwa devewoped by Johannes Rydberg in 1888, was created to describe de spectraw wines observed for Hydrogen. Rydberg's work expanded upon dis formuwa by awwowing for de cawcuwation of spectraw wines for muwtipwe different chemicaw ewements.[5] The deoreticaw importance granted to dese spectroscopic resuwts was greatwy expanded upon de devewopment of qwantum mechanics, as de deory awwowed for dese resuwts to be compared to atomic and mowecuwar emission spectra which had been cawcuwated a priori.

Whiwe radio astronomy was devewoped in de 1930s, it was not untiw 1937 dat any substantiaw evidence arose for de concwusive identification of an interstewwar mowecuwe[6] - up untiw dis point, de onwy chemicaw species known to exist in interstewwar space were atomic. These findings were confirmed in 1940, when McKewwar et aw. identified and attributed spectroscopic wines in an as-of-den unidentified radio observation to CH and CN mowecuwes in interstewwar space.[7] In de dirty years afterwards, a smaww sewection of oder mowecuwes were discovered in interstewwar space: de most important being OH, discovered in 1963 and significant as a source of interstewwar oxygen,[8] and H2CO (Formawdehyde), discovered in 1969 and significant for being de first observed organic, powyatomic mowecuwe in interstewwar space[9]

The discovery of interstewwar formawdehyde - and water, oder mowecuwes wif potentiaw biowogicaw significance such as water or carbon monoxide - is seen by some as strong supporting evidence for abiogenetic deories of wife: specificawwy, deories which howd dat de basic mowecuwar components of wife came from extraterrestriaw sources. This has prompted a stiww ongoing search for interstewwar mowecuwes which are eider of direct biowogicaw importance - such as interstewwar gwycine, discovered in 2009[10] - or which exhibit biowogicawwy rewevant properties wike Chirawity - an exampwe of which (propywene oxide) was discovered in 2016[11] - awongside more basic astrochemicaw research.

One particuwarwy important experimentaw toow in astrochemistry is spectroscopy drough de use of tewescopes to measure de absorption and emission of wight from mowecuwes and atoms in various environments. By comparing astronomicaw observations wif waboratory measurements, astrochemists can infer de ewementaw abundances, chemicaw composition, and temperatures of stars and interstewwar cwouds. This is possibwe because ions, atoms, and mowecuwes have characteristic spectra: dat is, de absorption and emission of certain wavewengds (cowors) of wight, often not visibwe to de human eye. However, dese measurements have wimitations, wif various types of radiation (radio, infrared, visibwe, uwtraviowet etc.) abwe to detect onwy certain types of species, depending on de chemicaw properties of de mowecuwes. Interstewwar formawdehyde was de first organic mowecuwe detected in de interstewwar medium.

Perhaps de most powerfuw techniqwe for detection of individuaw chemicaw species is radio astronomy, which has resuwted in de detection of over a hundred interstewwar species, incwuding radicaws and ions, and organic (i.e. carbon-based) compounds, such as awcohows, acids, awdehydes, and ketones. One of de most abundant interstewwar mowecuwes, and among de easiest to detect wif radio waves (due to its strong ewectric dipowe moment), is CO (carbon monoxide). In fact, CO is such a common interstewwar mowecuwe dat it is used to map out mowecuwar regions.[12] The radio observation of perhaps greatest human interest is de cwaim of interstewwar gwycine,[13] de simpwest amino acid, but wif considerabwe accompanying controversy.[14] One of de reasons why dis detection was controversiaw is dat awdough radio (and some oder medods wike rotationaw spectroscopy) are good for de identification of simpwe species wif warge dipowe moments, dey are wess sensitive to more compwex mowecuwes, even someding rewativewy smaww wike amino acids.

Moreover, such medods are compwetewy bwind to mowecuwes dat have no dipowe. For exampwe, by far de most common mowecuwe in de universe is H2 (hydrogen gas), but it does not have a dipowe moment, so it is invisibwe to radio tewescopes. Moreover, such medods cannot detect species dat are not in de gas-phase. Since dense mowecuwar cwouds are very cowd (10 to 50 K [−263.1 to −223.2 °C; −441.7 to −369.7 °F]), most mowecuwes in dem (oder dan hydrogen) are frozen, i.e. sowid. Instead, hydrogen and dese oder mowecuwes are detected using oder wavewengds of wight. Hydrogen is easiwy detected in de uwtraviowet (UV) and visibwe ranges from its absorption and emission of wight (de hydrogen wine). Moreover, most organic compounds absorb and emit wight in de infrared (IR) so, for exampwe, de detection of medane in de atmosphere of Mars[15] was achieved using an IR ground-based tewescope, NASA's 3-meter Infrared Tewescope Faciwity atop Mauna Kea, Hawaii. NASA's researchers use airborne IR tewescope SOFIA and space tewescope Spitzer for deir observations, researches and scientific operations.[16][17] Somewhat rewated to de recent detection of medane in de atmosphere of Mars. Christopher Oze, of de University of Canterbury in New Zeawand and his cowweagues reported, in June 2012, dat measuring de ratio of hydrogen and medane wevews on Mars may hewp determine de wikewihood of wife on Mars.[18][19] According to de scientists, "...wow H2/CH4 ratios (wess dan approximatewy 40) indicate dat wife is wikewy present and active."[18] Oder scientists have recentwy reported medods of detecting hydrogen and medane in extraterrestriaw atmospheres.[20][21]

Infrared astronomy has awso reveawed dat de interstewwar medium contains a suite of compwex gas-phase carbon compounds cawwed powyaromatic hydrocarbons, often abbreviated PAHs or PACs. These mowecuwes, composed primariwy of fused rings of carbon (eider neutraw or in an ionized state), are said to be de most common cwass of carbon compound in de gawaxy. They are awso de most common cwass of carbon mowecuwe in meteorites and in cometary and asteroidaw dust (cosmic dust). These compounds, as weww as de amino acids, nucweobases, and many oder compounds in meteorites, carry deuterium and isotopes of carbon, nitrogen, and oxygen dat are very rare on earf, attesting to deir extraterrestriaw origin, uh-hah-hah-hah. The PAHs are dought to form in hot circumstewwar environments (around dying, carbon-rich red giant stars).

Infrared astronomy has awso been used to assess de composition of sowid materiaws in de interstewwar medium, incwuding siwicates, kerogen-wike carbon-rich sowids, and ices. This is because unwike visibwe wight, which is scattered or absorbed by sowid particwes, de IR radiation can pass drough de microscopic interstewwar particwes, but in de process dere are absorptions at certain wavewengds dat are characteristic of de composition of de grains.[22] As above wif radio astronomy, dere are certain wimitations, e.g. N2 is difficuwt to detect by eider IR or radio astronomy.

Such IR observations have determined dat in dense cwouds (where dere are enough particwes to attenuate de destructive UV radiation) din ice wayers coat de microscopic particwes, permitting some wow-temperature chemistry to occur. Since hydrogen is by far de most abundant mowecuwe in de universe, de initiaw chemistry of dese ices is determined by de chemistry of de hydrogen, uh-hah-hah-hah. If de hydrogen is atomic, den de H atoms react wif avaiwabwe O, C and N atoms, producing "reduced" species wike H2O, CH4, and NH3. However, if de hydrogen is mowecuwar and dus not reactive, dis permits de heavier atoms to react or remain bonded togeder, producing CO, CO2, CN, etc. These mixed-mowecuwar ices are exposed to uwtraviowet radiation and cosmic rays, which resuwts in compwex radiation-driven chemistry.[22] Lab experiments on de photochemistry of simpwe interstewwar ices have produced amino acids.[23] The simiwarity between interstewwar and cometary ices (as weww as comparisons of gas phase compounds) have been invoked as indicators of a connection between interstewwar and cometary chemistry. This is somewhat supported by de resuwts of de anawysis of de organics from de comet sampwes returned by de Stardust mission but de mineraws awso indicated a surprising contribution from high-temperature chemistry in de sowar nebuwa.

Transition from atomic to mowecuwar gas at de border of de Orion mowecuwar cwoud.[24]

Research is progressing on de way in which interstewwar and circumstewwar mowecuwes form and interact, e.g. by incwuding non-triviaw qwantum mechanicaw phenomena for syndesis padways on interstewwar particwes.[25] This research couwd have a profound impact on our understanding of de suite of mowecuwes dat were present in de mowecuwar cwoud when our sowar system formed, which contributed to de rich carbon chemistry of comets and asteroids and hence de meteorites and interstewwar dust particwes which faww to de Earf by de ton every day.

The sparseness of interstewwar and interpwanetary space resuwts in some unusuaw chemistry, since symmetry-forbidden reactions cannot occur except on de wongest of timescawes. For dis reason, mowecuwes and mowecuwar ions which are unstabwe on Earf can be highwy abundant in space, for exampwe de H3+ ion, uh-hah-hah-hah. Astrochemistry overwaps wif astrophysics and nucwear physics in characterizing de nucwear reactions which occur in stars, de conseqwences for stewwar evowution, as weww as stewwar 'generations'. Indeed, de nucwear reactions in stars produce every naturawwy occurring chemicaw ewement. As de stewwar 'generations' advance, de mass of de newwy formed ewements increases. A first-generation star uses ewementaw hydrogen (H) as a fuew source and produces hewium (He). Hydrogen is de most abundant ewement, and it is de basic buiwding bwock for aww oder ewements as its nucweus has onwy one proton. Gravitationaw puww toward de center of a star creates massive amounts of heat and pressure, which cause nucwear fusion. Through dis process of merging nucwear mass, heavier ewements are formed. Carbon, oxygen and siwicon are exampwes of ewements dat form in stewwar fusion, uh-hah-hah-hah. After many stewwar generations, very heavy ewements are formed (e.g. iron and wead).

On August 29, 2012, and in a worwd first, astronomers at Copenhagen University reported de detection of a specific sugar mowecuwe, gwycowawdehyde, in a distant star system. The mowecuwe was found around de protostewwar binary IRAS 16293-2422, which is wocated 400 wight years from Earf.[29][30] Gwycowawdehyde is needed to form ribonucweic acid, or RNA, which is simiwar in function to DNA. This finding suggests dat compwex organic mowecuwes may form in stewwar systems prior to de formation of pwanets, eventuawwy arriving on young pwanets earwy in deir formation, uh-hah-hah-hah.[31]

For de study of de recourses of chemicaw ewements and mowecuwes in de universe is devewoped de madematicaw modew of de mowecuwes composition distribution in de interstewwar environment on dermodynamic potentiaws by professor M.Yu. Dowomatov using medods of de probabiwity deory, de madematicaw and physicaw statistics and de eqwiwibrium dermodynamics.[38][39][40] Based on dis modew are estimated de resources of wife-rewated mowecuwes, amino acids and de nitrogenous bases in de interstewwar medium. The possibiwity of de oiw hydrocarbons mowecuwes formation is shown, uh-hah-hah-hah. The given cawcuwations confirm Sokowov’s and Hoyw’s hypodeses about de possibiwity of de oiw hydrocarbons formation in Space. Resuwts are confirmed by data of astrophysicaw supervision and space researches.